From 6b2f3d1f769be5779b479c37800229d9a4809fc3 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Tue, 27 Oct 2009 11:05:28 +0100 Subject: vfs: Implement proper O_SYNC semantics While Linux provided an O_SYNC flag basically since day 1, it took until Linux 2.4.0-test12pre2 to actually get it implemented for filesystems, since that day we had generic_osync_around with only minor changes and the great "For now, when the user asks for O_SYNC, we'll actually give O_DSYNC" comment. This patch intends to actually give us real O_SYNC semantics in addition to the O_DSYNC semantics. After Jan's O_SYNC patches which are required before this patch it's actually surprisingly simple, we just need to figure out when to set the datasync flag to vfs_fsync_range and when not. This patch renames the existing O_SYNC flag to O_DSYNC while keeping it's numerical value to keep binary compatibility, and adds a new real O_SYNC flag. To guarantee backwards compatiblity it is defined as expanding to both the O_DSYNC and the new additional binary flag (__O_SYNC) to make sure we are backwards-compatible when compiled against the new headers. This also means that all places that don't care about the differences can just check O_DSYNC and get the right behaviour for O_SYNC, too - only places that actuall care need to check __O_SYNC in addition. Drivers and network filesystems have been updated in a fail safe way to always do the full sync magic if O_DSYNC is set. The few places setting O_SYNC for lower layers are kept that way for now to stay failsafe. We enforce that O_DSYNC is set when __O_SYNC is set early in the open path to make sure we always get these sane options. Note that parisc really screwed up their headers as they already define a O_DSYNC that has always been a no-op. We try to repair it by using it for the new O_DSYNC and redefinining O_SYNC to send both the traditional O_SYNC numerical value _and_ the O_DSYNC one. Cc: Richard Henderson Cc: Ivan Kokshaysky Cc: Grant Grundler Cc: "David S. Miller" Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: Thomas Gleixner Cc: Al Viro Cc: Andreas Dilger Acked-by: Trond Myklebust Acked-by: Kyle McMartin Acked-by: Ulrich Drepper Signed-off-by: Christoph Hellwig Signed-off-by: Andrew Morton Signed-off-by: Jan Kara --- arch/alpha/include/asm/fcntl.h | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) (limited to 'arch/alpha') diff --git a/arch/alpha/include/asm/fcntl.h b/arch/alpha/include/asm/fcntl.h index 25da0017ec87..21b1117a0c61 100644 --- a/arch/alpha/include/asm/fcntl.h +++ b/arch/alpha/include/asm/fcntl.h @@ -1,8 +1,6 @@ #ifndef _ALPHA_FCNTL_H #define _ALPHA_FCNTL_H -/* open/fcntl - O_SYNC is only implemented on blocks devices and on files - located on an ext2 file system */ #define O_CREAT 01000 /* not fcntl */ #define O_TRUNC 02000 /* not fcntl */ #define O_EXCL 04000 /* not fcntl */ @@ -10,13 +8,28 @@ #define O_NONBLOCK 00004 #define O_APPEND 00010 -#define O_SYNC 040000 +#define O_DSYNC 040000 /* used to be O_SYNC, see below */ #define O_DIRECTORY 0100000 /* must be a directory */ #define O_NOFOLLOW 0200000 /* don't follow links */ #define O_LARGEFILE 0400000 /* will be set by the kernel on every open */ #define O_DIRECT 02000000 /* direct disk access - should check with OSF/1 */ #define O_NOATIME 04000000 #define O_CLOEXEC 010000000 /* set close_on_exec */ +/* + * Before Linux 2.6.32 only O_DSYNC semantics were implemented, but using + * the O_SYNC flag. We continue to use the existing numerical value + * for O_DSYNC semantics now, but using the correct symbolic name for it. + * This new value is used to request true Posix O_SYNC semantics. It is + * defined in this strange way to make sure applications compiled against + * new headers get at least O_DSYNC semantics on older kernels. + * + * This has the nice side-effect that we can simply test for O_DSYNC + * wherever we do not care if O_DSYNC or O_SYNC is used. + * + * Note: __O_SYNC must never be used directly. + */ +#define __O_SYNC 020000000 +#define O_SYNC (__O_SYNC|O_DSYNC) #define F_GETLK 7 #define F_SETLK 8 -- cgit v1.2.2